An alkylation process, which is disclosed in U.S. Pat. No. 7,432,408 (“the '408 patent”), involves contacting isoparaffins, preferably isopentane, with olefins, preferably ethylene, in the presence of an ionic liquid catalyst to produce gasoline blending components. The contents of the '408 patent are incorporated by reference herein in its entirety.
An ionic liquid catalyst distinguishes this novel alkylation process from conventional processes that convert light paraffins and light olefins to more lucrative products such as the alkylation of isoparaffins with olefins and the polymerization of olefins. For example, two of the more extensively used processes to alkylate isobutane with C3-C5 olefins to make gasoline cuts with high octane numbers use sulfuric acid (H2SO4) and hydrofluoric acid (HF) catalysts.
As a result of use, ionic liquid catalysts can become deactivated, i.e. lose activity, and may eventually need to be replaced. Alkylation processes utilizing an ionic liquid catalyst can form by-products known as conjunct polymers. These conjunct polymers generally deactivate the ionic liquid catalyst by forming complexes with the ionic liquid catalyst. Conjunct polymers are highly unsaturated molecules and can complex the Lewis acid portion of the ionic liquid catalyst via their double bonds. For example, as aluminum trichloride in aluminum trichloride-containing ionic liquid catalysts becomes complexed with conjunct polymers, the activity of these ionic liquid catalysts becomes impaired or at least compromised. Conjunct polymers may also become chlorinated and through their chloro groups may interact with aluminum trichloride in aluminum trichloride-containing catalysts and therefore reduce the overall activity of these catalysts or lessen their effectiveness as catalysts for their intended purpose.
Deactivation of ionic liquid catalysts by conjunct polymers is not only problematic for alkylation chemistry, but also affects the economic feasibility of using ionic liquid catalysts as they are expensive to replace. Therefore, commercial exploitation of ionic liquid catalysts in alkylation is economically infeasible unless they can be efficiently regenerated and recycled.
A few methods for regenerating ionic liquid catalysts, which involve removing conjunct polymers from the catalysts, have been devised. These regeneration methods involve hydrogenation of the conjunct polymers, addition of a reagent capable of replacing the complexed conjunct polymers, and alkylation of the conjunct polymers.
Regeneration methods involving hydrogenation of the conjunct polymers are described in U.S. Patent Application Publication Nos. 2007/0142218 (“the '218 publication”), 2007/0142217 (“the '217 publication”), 2007/0142215 (“the '215 publication”), 2007/0142214 (“the '214 publication”), and 2007/0142213 (“the '213 publication”). The '218 publication is directed to a process for regenerating a used acidic ionic liquid catalyst comprising the steps of contacting the used ionic liquid catalyst and hydrogen with a homogeneous hydrogenation catalyst in a reaction zone under hydrogenation conditions for a time sufficient to increase the activity of the used catalyst. The '217 publication is directed to a process for regenerating a used acidic ionic liquid catalyst which has been deactivated by conjunct polymers comprising combining the used catalyst, a metal, and a Broensted acid which acts as a source of hydrogen in a reaction zone under hydrogenation conditions for a time sufficient to hydrogenate at least a portion of the conjunct polymer. The '215 publication relates to a process for regenerating a used acidic ionic liquid catalyst comprising the steps of contacting the used ionic liquid catalyst and hydrogen with a supported hydrogenation catalyst comprising a hydrogenation component on a support in a reaction zone under hydrogenation conditions for a time sufficient to increase the activity of the used catalyst. The '214 publication relates to a process for regenerating a used acidic ionic liquid catalyst which has been deactivated comprising the steps of contacting the used chloroaluminate ionic liquid catalyst and hydrogen with a metal hydrogenation catalyst in a reaction zone under hydrogenation conditions for a time sufficient to increase the activity of the ionic liquid catalyst. The '213 publication relates to a process for regenerating a used acidic catalyst which has been deactivated by conjunct polymers by removing the conjunct polymers so as to increase the activity of the catalyst. The '213 publication discusses hydrogenation as one method of removing the conjunct polymers.
Regeneration methods involving the addition of a reagent capable of replacing the complexed conjunct polymers are described in the '213 publication and U.S. Patent Application Publication No. 2007/0142211 (“the '211 publication”). As discussed above, the '213 publication relates to a process for regenerating a used acidic catalyst which has been deactivated by conjunct polymers by removing the conjunct polymers so as to increase the activity of the catalyst. The '213 publication discusses addition of a basic reagent as another method of removing the conjunct polymers. The '211 publication is directed to a process for regenerating a used ionic liquid catalyst comprising a cationic component and an anionic component, which catalyst has been deactivated by conjunct polymers complexed with the anionic component comprising the steps of adding a reagent which is capable of replacing the complexed conjunct polymer with the cationic component of the catalyst, said reagent being added in an amount sufficient to increase the activity of the used ionic liquid catalyst.
A regeneration method involving alkylation of the conjunct polymers is described in the '213 publication and U.S. Patent Application Publication No. 2007/0142216 (“the '216 publication”). As discussed above, the '213 publication relates to a process for regenerating a used acidic catalyst which has been deactivated by conjunct polymers by removing the conjunct polymers so as to increase the activity of the catalyst. The '213 publication discusses alkylation as yet another method of removing the conjunct polymers. The '216 publication relates to a process for regenerating a used acidic ionic liquid catalyst comprising contacting the used ionic liquid catalyst with an isoparaffin-containing stream and Broensted acid in a reaction zone under alkylation conditions for a time sufficient to increase the activity of the ionic liquid catalyst.
Additional methods of regenerating a used or spent acidic ionic liquid catalyst involve contacting the used catalyst with a regeneration metal in the presence or absence of hydrogen. Such methods are described in U.S. Patent Application Publication Nos. 2007/0249486 (“the '486 publication”) and 2007/024985 (“the '485 publication”). The '486 publication relates to a process for regenerating a used acidic ionic liquid catalyst comprising contacting the used ionic liquid catalyst with at least one regeneration metal in a regeneration zone in the presence of added hydrogen under regeneration conditions for a time sufficient to increase the activity of the ionic liquid catalyst. The '485 publication relates to a process for regenerating a used acidic ionic liquid catalyst comprising contacting the used ionic liquid catalyst with at least one metal in a regeneration zone in the absence of added hydrogen under regeneration conditions for a time sufficient to increase the activity of the ionic liquid catalyst.
However, while effective, each of these methods suffers from certain shortcomings. Thus, to take advantage of the potential of ionic liquids as catalysts, particularly in alkylation reactions, the industry continues to search for an effective and efficient process for removing conjunct polymers from ionic liquid catalysts to thereby regenerate the ionic liquid catalysts. In general, the process should be simple and efficient enough to be used to remove conjunct polymers from an ionic liquid catalyst quickly and effectively.